References

M., Linford, L. S., et al. 1997. Evidence for a clade of nematodes, arthropods and other moulting animals. Nature 387, 489-493. Albertson, D. G. & Thomson, J. N. 1993. Segregation of holocentric chromosomes at meiosis in the nematode Caenorhabditis elegans. Chromosome Research 1, 15-26. Basham, S. E. & Rose, L. S. 2001. Caenorhabditis elegans embryo establishment of asymmetry. In Encyclopedia of Life Sciences. Chichester Wiley. www.els.net. Bischoff, M....

Evolution of neurogenesis in arthropods

Several alternative hypotheses have been suggested that support various phylogenetic groupings of the individual euarthropod taxa, the chelicerates, myriapods, crustaceans and insects. The Tetraconata hypothesis suggests a sister-group relationship of insects and crustaceans in contrast to the traditional monophyletic grouping of myria-pods and insects, the Tracheata or Atelocerata (see references in Stollewerk and Chipman 2006). The Mandibulata hypothesis suggests a clade consisting of...

Thoughts and speculations on the ancestral arthropod segmentation pathway

In the past decade or so, there has been a significant increase in the available data on the developmental mechanisms underlying the process of segmentation in a wide range of arthropod taxa. This large body of data makes it possible to attempt, albeit cautiously, a comparative analysis of the various aspects of the segmentation process, and to try to find which of its features and components may have been present in the arthropod common ancestor. A recent review (Peel et al. 2005) covers much...

Basal euarthropod development a fossilbased perspective

Nigel c. hughes, joachim t. haug and dieter waloszek The morphological gap between Euarthropoda (the crown group that contains all extant arthropods) and living arthropod-like animals such as onychophorans, tardigrades and pentastomids is bridged by a number of fossils known primarily from rocks some 520 to 490 million years old (e.g. Fuxianhuia, Chengjiangocaris, Shankouia, see Figure 15.1 cf. Waloszek et al. 2005). These centimetre-scale fossil animals illuminate critical steps in early...

Stem Crown

Figure 12.1 Conflicting phylogenies and scenarios on the nature and origin of the Last Common Ancestor (LCA) of the Bilateria, also featuring the extent of stem and crown groups. A, The complex Urbilateria scenario features a large, complex ancestor bearing most characters of present-day bilaterians (characters 1-9, and eventually characters 10-11 in Table 12.1). This ancestor originated from either an adult (polyp) or a larval radial cnidarian (archicoelomate theory, originally proposed by...

Nkl

However, the Msx4 gene (now called MSX2P Genbank accession NR_002307) that is linked to the HOXB cluster in humans is a processed pseudogene, and has been dismissed as useless for reconstructing ancestral linkage patterns (Castro and Holland 2003). It is still intriguing, however, that of all of the places in the genome that an Msx processed pseudogene could jump into, it should happen to land right next to a Hox cluster, within 10 Mb. The Mega-homeobox...

Imhh

Ancestral genes + non-canonical seq. evol. Figure 10.1 The diversity of the Hox-linked and NK-linked genes was already established early in animal evolution, but were the genes linked in a Mega-homeobox cluster or not Conventionally a distinction has been made between Hox-like and NK-like (NKL) genes in the ANTP-class. However, the boundary between these two groups is very fuzzy, with poorly resolved molecular phylogenetic trees of homeodomain sequences. The coloration used here instead...

Info

Either way, cuticle, sporopollenin-coated spores and stomata are considered to be key innovations that conferred desiccation resistance on vegetative and reproductive structures, and so assisted in the colonisation of land (reviewed in Cronk 2001). The earliest land plants were bryophytes (mosses, liverworts and hornworts), and extant bryophytes form a paraphyletic grade at the base of land-plant phylogenies (Wellman et al. 2003, Qiu et al. 2006). Recent evidence points to the hornworts as the...

Lbx

TLX2 (HOX11L1, NCX, Enx, Tlx2), TLX3 (HOX11L2, RNX) NK1slou NKX1-1 (HSPX153, SAX1, NKX1.1), NKX1-2 (NKX1.2, SAX2) ladybird early (lbe), ladybird late (lbl) C15 (93Bal, clawless, Hox11-311, Ect5) slouch (slou) (paired-like9, S59, NK-1) AmphiNK1a & b, NveNK1 NveSLOU PduNK1

Mega Evolution In Zoology

Evolution of the gene network underlying wing polyphenism in ants. Science 297, 249-252. Amundson, R. 2005. The Changing Role of the Embryo in Evolutionary Thought Roots of Evo-Devo. Cambridge Cambridge University Press. Ankeny, R. A. 2001. Model organisms as models understanding the 'Lingua Franca' of the human genome project. Philosophy of Science 68, S251-S261. Arthur, W. 1997. The Origin of Animal Body Plans. A Study in Evolutionary Developmental Biology....

Genetic Information

Figure 5.4 Possible representations of the multidimensional space controlling gene regulation in eukaryotic cells. A, Individual genetic elements (black circles) interact with many other elements through positive and negative interactions (activation and repression arrows, respectively) quantitative aspects of these interactions are represented by variable thicknesses (strength of the interaction) and lengths (duration of the interaction) of the interaction arrows. B, As a concept diagram,...

Plants are used to having identity crises

Rolf rutishauser, valentin grob and evelin pfeifer Macroscopic nature is never really anomalous. Abnormalities, like other exceptional cases, at least show incontestably, what the plants can do. However, regardless of how much faith one has in anatomical definitions, they should not be taken as more than a means of communication prior to subsequent genetic analysis. Truth, except as a figure of speech, does not exist in empirical science. Our green and living world is a continuum in space and...

The Impact Of Evodevo On Evolutionary Theory

The conceptual framework of evo-devo arose as a response to the incompleteness of the neo-Darwinian synthesis (Callebaut et al. 2007). The paradigm of the synthesis was based on the correlation of phenotypic character variation with statistical changes of gene frequencies in populations. Adaptive change as a population genetic event was the explanandum. The paradigm of evo-devo, by contrast, represents a causal-mechanistic approach towards the explanation of phenotypic change in evolution. Here...

On comparisons and causes in evolutionary developmental biology

Denn mit dem Warum der Dinge kommt niemand zu Ende. Die Ursachen alles Geschehens gleichen den D nenkulissen am Meere eine ist immer der anderen vorgelagert, und das Weil, bei dem sich ruhen lie e, liegt im Unendlichen. For once you begin with the Why you can never get to the end. It is like the dunes by the sea, where behind each dune lies still another and the Because where you might come to final rest lies somewhere in infinity. Thomas Mann, Joseph und seine Br der Comparison is fundamental...

Unravelling body plan and axial evolution in the Bilateria with molecular phylogenetic markers

Jaume baguna, pere martinez, jordi paps and marta riutort setting the problem The emergence of dramatic morphological differences (disparity) and the ensuing bewildering increase in the number of species (diversity) documented in the fossil record at key stages of animal and plant evolution have defied, and still defy, the explanatory powers of Darwin's theory of evolution by natural selection. Among the best examples that have captured the imagination of the layman and the interest of scores...

Evolving body features

'Distinctive features', 'key apomorphies', 'novelties', 'innovations'. All these terms point to the fact that some characters in an organism are 'special' in some respect, and these have attracted the most interest from biologists and challenged the explanatory capacity of evolutionary theories. These are characters that emerged as new features during the evolution of a lineage, or that are believed to be the principal cause of a successful phyletic radiation. 'Evolution is tinkering' and in...

Arthropod appendages a prime example for the evolution of morphological diversity and innovation

Nikola-michael prpic and wim g. m. damen The morphology of the appendages of the arthropods has been adapted to a large number of life styles that is virtually unparalleled in any other organ in the Metazoa. Different appendage types exist e.g. for walking, swimming, jumping, prey-capture, chewing, biting, mating, egg-laying, breathing in air, fresh water and salt water, and sensory perception see Figure 20.1 for examples . Very specialised appendage types exist for specialised modes of life...

A pragmatic approach for selecting evodevo model species in amniotes

Athanasia c. tzika and michel c. milinkovitch One major classical justification of using a model metazoan species for experimentation has been that discoveries of biological phenomena in that species could be extrapolated to other multicellular species. Because the chances that this extrapolation is valid in humans depend on the phylogenetic distance between humans and the model species, many researchers have somewhat sacrificed the major benefits of small size, short generation time and ease...

Prospects of evodevo for linking pattern and process in the evolution of morphospace

Evolutionary developmental biology or evo-devo will make crucial contributions over the coming years to exploring the occupancy of mor-phospace. Why do species show the patterns of diversity and disparity they do, and to what extent do such patterns reflect the ways in which phenotypic variation is generated as well as the processes of natural selection Evo-devo in appropriate study systems is providing the means to explore fully how phenotypic variation is generated by the processes intrinsic...

Are transposition events at the origin of the bilaterian Hox complexes

The genome sequences of two non-bilaterian animals, the cnidarians NematosteUa vectensis and Hydra magnipapillata, have been recently completed. These new data lead to the fascinating result that the complement of Hox genes in the cnidarian ancestor is considerably lower than that in the bilaterians, although the complexity of their genome is otherwise similar Technau et al. 2005 . Thus, there is a correlation between the radiation of the Bilateria and the expansion of the Hox complex. In the...

Chiparian Planula

Bra. -cat. obi. chd gtc, bmp5-8 ash Figure 12.4 Comparative axial expression, in a simplified form, of key developmental genes between cnidarians planula larva, top left, and polyp, bottom left and bilaterians right . In the planula larva genes expressed asymmetrically along the directive axis 'D-V' axis are also depicted. A anterior AB aboral D dorsal O oral P posterior V ventral. 'D' and 'V' imply the likely, but still undefined, DV character of the directive axis in...

Conflicting hypotheses on the nature of megaevolution

Parasitic Platyhelminthes

Here is a question of the utmost importance for our understanding ofwhat has been called the 'big picture' of evolution Simpson 1944,1953 are the divergences that lead ultimately to high-level sister groups, such as those that would typically be labelled as orders, classes and phyla, qualitatively or quantitatively different from those that lead to low-level sister groups, such as races, species and genera In other words, is megaevolution more than just accumulated micro macro-evolution, or...